1. Field of the Invention
The present invention relates to improved melt-flow liquid crystalline polymer compositions (LCPs) with unusually high toughness.
2. Background of the Invention
Liquid crystalline polymer compositions are known in the art by various terms, including "liquid crystal" and "anisotropic melts." LCPs are known to have exceptionally high tensile strength and modulus compared to analogous polymers not having a liquid crystalline character. LCPs are useful in many applications, including molding resins for a variety of electrical parts, and for other uses such as films. While LCPs are known for their ability to flow under difficult molding conditions, in some instances such as for encapsulating electronic components, the melt viscosities of normal molding grade LCPs are too high.
Generally speaking, the mclt viscosity of any given LCP is most affected by the polymer molecular weight, the lower the molecular weight the lower the melt viscosity. While low molecular weight LCPs can be synthesized directly by condensation polymerization, this method may have some drawbacks. The polymer produced may have a tendency to increase in molecular weight (MW) during melt processing by continuation of the melt condensation process. At extremely low viscosity levels of 50 Pa*s or less, these LCPs are very brittle. Additionally, the handling of such low molecular weight polymers in processes designed to produce molding grade polymers can be problematical. European Patent Application 376,615 describes a method of preparing a LCP with a relatively low melt viscosity by mixing 100 parts of a high molecular weight LCP with 1-100 parts, preferably 10-40 parts, of a low molecular weight LCP with a MW about 1000 to 7000, preferably between 1000-4000. This method requires production of an unusual low molecular weight LCP using special equipment, since the low molecular weight LCP material is not readily commercially available at a MW range of 1000 to 7000.
U.S. Pat. No. 4,434,262 describes an improved melt processable blend of a major amount of polyester or polyolefin with a low MW liquid crystalline compound preferably below 1000 molecular weight. The liquid crystalline compound does not chemically react with the polyolefin or the polyester component in the melt blend. Melt viscosity reductions of 25% to 75% were obtained by adding 10 parts by weight of the liquid crystalline compound to 90 parts by weight of polyolefin or polyester.
Accordingly, it is an object of this invention to provide a method for improving the melt viscosity or fluidity of an LCP, as well as an LCP resin composition having improved melt-viscosity, or fluidity, that can be efficiently fabricated into an article having a small thickness or an intricate shape at lower processing temperatures, while still maintaining the original strength, rigidity, and elongation characteristics of the parent LCP.